In the industrial world, various kinds of apparatuses have existed which are configured so that the inside of a space airtightly-shielded from the outside is kept to a pressure state different from the outside pressure, that is, kept under a differential pressure state and various kinds of treatments are allowed to be performed under the differential pressure state. In some cases, various kinds of treatments are performed while the inside of the space is kept to a dust-proof state or a special gas environmental state in addition to the differential pressure state. For example, predetermined treatments are performed under a vacuum-evacuated dust-proof state in an evacuating processing apparatus for semiconductor wafers, a vacuum dryer, a rotating anticathode type X-ray generator, an electron microscope or the like. A magnetic fluid sealing apparatus is used to shield two areas of a space area (the inside of an airtight chamber) for performing these predetermined treatments and an atmosphere pressure area from each other.
A conventional magnetic fluid sealing apparatus is configured so that bearings are incorporated in the inner walls the neighborhood of both the ends of a cylindrical housing, and the rotating shaft is freely rotatably supported by these bearings. Furthermore, the conventional magnetic fluid sealing apparatus is configured so that a magnet is contained in the housing and magnetic fluid is filled in the gap between the magnet and the rotating shaft to enhance hermetical sealing. The magnetic fluid is held in the gap between the magnet and the rotating shaft by magnetic field occurring around the magnet.
Patent Document 1 discloses a conventional magnetic fluid sealing apparatus having a structure of this type.
Since the magnetic fluid sealing apparatus contains the magnet as described above, magnetic field unavoidably occurs around the magnet. However, a target apparatus to which the magnetic fluid sealing apparatus is applied has a risk that the performance of the target apparatus is adversely affected by the magnetic field. For example, this occurs in such a case that an electron microscope using an electron beam, an X-ray generator for making electrons from an electron gun impinge against an anticathode (target) to generate X-ray from the surface of the anticathode or the like is used as the target apparatus. In these apparatuses, electrons are treated in an airtight chamber, and thus when magnetic field generated by the magnet of the magnetic fluid sealing apparatus leaks into the airtight chamber of the target apparatus, there is a concern about such an adverse effect that the trajectory of electrons is deviated from an original trajectory by the leaking magnetic field or the like.